Investigation of audition in mammals is often difficult and complex due to the complex nature of the auditory system in these species. It has been established, however, that studies of the auditory system in lower vertebrates can be of considerable value in understanding the function of the auditory system in all vertebrates. One system that is showing value in providing insight into audition in other vertebrates is the auditory system in fish. The present study is directed towards obtaining insight into basic mechanisms of teleost audition since such data are necessary in order to use these species for other studies more directly related to mammalian audition. The present studies are directed to understanding the role of the peripheral portions of the auditory system in fishes and include detailed analyses of the roles of specific structures in sound processing. Physiological and behavioral techniques will be used. Specific questions relate to (a) the role of the inner ear in sound detection and processing, (b) the response characteristics of single neurons in the auditory nerve, (c) the mechanisms of hair cell stimulation in the inner ear and determination of sound source direction (localization), (d) the role of the swim bladder in detection and processing of signals, (e) the contributions of the Weberian ossicles in signal processing, (f) behavioral detection capabilities to pure tones and determination of ranges of sounds that can be detected by different teleost species, and (g) mechanisms of processing and the levels of the auditory system at which signals are analyzed.